The climate is the average of the dynamic processes in the earth's atmosphere determined using meteorological methods , based on small-scale locations ( meso or regional climate) or on continental dimensions ( macroclimate ), including all fluctuations in the course of the year and based on a large number of climate elements . The climatic conditions are not only controlled by solar radiation and the physical and chemical processes within the atmosphere, but also by the influences and interactions of the other four earth spheres (Hydrosphere , cryosphere , biosphere and lithosphere ). In order to show the temperature profile in a statistically relevant time frame with sufficient accuracy in addition to all other weather processes, the World Meteorological Organization (WMO) recommends the use of reference periods (including normal periods or CLINO periods ) in which the monthly mean values as a time series over 30 years in one Dataset are summarized. The reference period from 1961 to 1990 is currently the valid and commonly used benchmark. After 2021, this will be replaced by the new normal period 1991 to 2020.
The regularities of the climate, its components, processes and influencing factors as well as its possible future development are the subject of research in climatology . As an interdisciplinary science, climatology cooperates with subjects such as physics , meteorology , geography , geology and oceanography and uses some of their methods or detection methods.
The paleoclimatology is a significant portion of both the climatology and the Historical Geology . Your task is to use isotope examinations and data series from climate archives and indirect climate indicators ( proxies ) to reconstruct the climatic conditions over historical or geological periods in the form of a climate history and to decipher the mechanisms of past climate change events, such as the influence of periodic climate change changing solar radiation due to the Milanković cycles on the earth system.
Depending on the stage of development and the focus of climate research, there were and are different definitions. The Intergovernmental Panel on Climate Change (IPCC) works on the basis of a broad definition:
“Climate in the narrower sense is usually defined as the average weather, or more precisely as the statistical description in the form of the average and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classic period for averaging these variables is 30 years as defined by the World Meteorological Organization. The relevant parameters are mostly surface variables such as temperature, precipitation and wind. Climate in the broader sense is the condition, including a statistical description, of the climate system. "
This definition of the IPCC includes a deep-time perspective and takes into account other subsystems ( earth spheres ) in addition to the atmosphere . It reflects the development since the second half of the 20th century, when interdisciplinary research into climate dynamics, including its causes, became possible and came to the fore. Thus the temporal dimension gained importance compared to the regional dimension.
The German Weather Service (DWD) defines climate more closely, with spatial reference and on a time scale of decades:
“The climate is defined as the summary of the weather phenomena that characterize the mean state of the atmosphere at a certain location or in a more or less large area.
It is represented by the overall statistical properties (mean values, extreme values, frequencies, duration values, etc.) over a sufficiently long period of time. In general, a period of 30 years is used as a basis, the so-called normal period, but shorter periods are also used. "
In the geographic Climatology Climate of Joachim Blüthgen in his was general climatology defined as follows:
"The geographical climate is the typical summary of the near-earth and the earth's surface influencing atmospheric conditions and weather processes over a long period of time in a characteristic frequency distribution for a place, a landscape or a larger area."
In meteorological climatology, the climate according to Manfred Hendl is defined as follows:
"Climate is the locally characteristic frequency distribution of atmospheric conditions and processes during a sufficiently long reference period, which is to be selected so that the frequency distribution of the atmospheric conditions and processes does justice to the typical conditions at the reference location."
The fundamental definition for climatology comes from the Viennese meteorologist Julius von Hann (1839–1921), who understood the term as "the totality of all meteorological phenomena that characterize the mean state of the atmosphere at any point on the earth's surface." (Handbuch der Klimatologie, 1883) With this, von Hann founded the "mean climatology". In his definition he went back to the 19th century definition by Alexander von Humboldt , which aimed at the human experience of a place ; he understood climate as “all changes in the atmosphere that noticeably affect our organs” ( Cosmos Volume I ).
The word climate ( plural : Klimate or, closer to the Greek , Klimata ; rarely ( Germanized ) also Klimas ) is a takeover of the ancient Greek word κλίμα klíma , whose first meaning (around 500 BC ) in this context 'curvature / inclination [ of the position of the sun] 'and belongs to the verb κλίνειν klínein ,' incline ',' bend ',' curve ',' lean '. The term finally came into German via the late Latin clima (verb: clinare , ' beugen ', ' biegen ', ' neigen ') .
Climate does not refer to the ecliptic , i.e. to the fact that the earth's axis has an inclination angle of approx. 23.5 degrees to the plane of the earth's orbit , but to the spherical shape of the earth. This corresponds to the experience that it is only possible to observe other regions of the sky by moving in a north-south direction. The corresponding Germanization is the compound " Himmelsstrich ", which, however, only describes the geographical area and no longer the associated weather.
In contrast to the weather occurring in a certain area (time frame: hours to a few days) and the weather (time frame: up to about a week, less often a month or a season), firmly defined periods of time are statistically evaluated in climatology, primarily in relation to the 19th through the 21st centuries. The starting point is always the weather, including the meteorologically recorded data and measured values.
The World Meteorological Organization (WMO) recommends so-called normal climate periods with a duration of 30 years. The current standard is the year series 1961–1990, which according to the usual rules is valid until at least 2020 and is then replaced by 1991–2020. Alternative normal periods are also used for practical reasons. In order to have as timely an interval as possible, the Austrian Central Institute for Meteorology and Geodynamics (ZAMG) often uses the period 1971–2000, also with regard to the glacier inventories that are important for the Alpine region . In addition, the WMO recommends to its member organizations the comparison period 1981–2010, which serves as a data basis parallel to the reference period 1961–1990, including for MeteoSwiss .
In addition, larger periods of time, such as the hundred-year secular period 1851–1950, are evaluated in order to present climatic anomalies and trends in a larger temporal context. This principle is applied at both a local and a national or global level. The internationally recognized index of the Goddard Institute for Space Studies (GISS) and NASA contains the worldwide temperature anomalies from the year 1880 on the basis of the reference period 1951–1980.
In the case of climatic reconstructions that cover geological periods and thus periods of millions of years , weather influences naturally no longer play a role. Instead, an attempt is made to create climatic characteristics of the respective epochs, including short-term cooling or warming phases, by evaluating sediments, animal and plant fossils and through isotope studies. Due to the rapid progress of the various analysis techniques, increasingly more precise results are being achieved in this sector, including in terms of time resolution.
The term climate is often associated with the global climate or global climate. However, the global temperature development is not representative for individual regions, which can even show an opposite tendency over a certain period of time. An example of this is a stable cold bubble called a “cold blob” in the subpolar Atlantic south of Greenland , which evidently developed over decades and which may owe its existence to extensive meltwater discharges from the Greenland ice sheet . Conversely, a local record summer can "disappear" in globally determined data series.
With regard to spatial dimensions, a three-level classification has proven itself:
- The microclimate ranges from a few meters to a few kilometers, like a terrace, an agricultural area or a street.
- The mesoclimate refers to stretches of land (for example a mountain range) up to a few hundred kilometers.
- The macroclimate describes continental and global relationships.
While there is a close relationship between the spatial dimension and the duration of the event in weather , this aspect is less relevant for climatological analyzes.
Microclimate (or microclimate)
Microclimate refers to the climate in the area of the air layers close to the ground up to a height of about two meters or the climate that develops in a small, clearly defined area (for example on slopes or in an urban environment ).
The microclimate is decisively shaped by the surface structure and the ground friction of the wind that occurs there . In this environment there are weaker air currents, but greater temperature differences . The diversity of the soils , the landforms and the plant community can cause great climatic contrasts in a small space. The microclimate is ideal for low-growing plants is important because this most sensitive to climate Life stage through in the surface air layer, and plays for example, the properties of a vineyard in quality viticulture an important role.
Humans are also directly exposed to the microclimate. Especially in the living space of a city, the microclimate often deviates from the natural conditions due to different building materials , architectural design , solar radiation or shading and can change quickly and permanently through interventions in the respective building fabric or its surroundings.
Mesoclimate consists of different individual climates that are between a few hundred meters and a few hundred kilometers, but usually include areas in the lower kilometer range. Because of this broad but local spectrum, many aspects of applied meteorology and climatology play a major role, for example the urban climate or the rainforest climate . In general, all local climates and terrain climates are counted as mesoclimates, like the local climates of ecosystems , whereby the transition to microclimates is fluid in these.
The regional climate is the climate of a unit of space on the mesoscale. Accordingly, it has a lot in common with the mesoclimate . The regional climate is characterized by the fact that it depends primarily on regional conditions such as land use. In addition, the regional shape of the terrain is an important influencing factor.
As the regional climate is particularly important for forestry, agricultural and infrastructural processes, regional climate maps are used for this. Normally one examines regional climates in relation to geographically, administratively or scenically delimited territorial units.
Macroclimate (or large-scale climate)
Macroclimates include large-scale atmospheric circulation patterns, ocean currents or climate zones of more than 500 kilometers. These include the flow combination of the thermohaline circulation , which unites four of the five oceans into one water cycle, as well as the periodic effects of the Atlantic multi-decade oscillation . The various wind systems of the planetary circulation , for example the monsoons , the trade winds or the oceanic and atmospheric Rossby waves , are assigned to the macroclimate, as are large regional climates such as the Amazon rainforest . All macroclimates influence each other and together form the global climate system.
Climate zones and climate classification
Areas with the same climatic conditions are divided into climatic zones and thus classified. The best-known classification comes from the geoscientist Wladimir Köppen (1846–1940). His work Geographisches System der Klimate , published in 1936, is considered to be the first objective climate classification (see illustration on the right). It was widely used primarily through Köppen's collaboration with climatologist Rudolf Geiger and is still very important today.
The extent, structure and location of the climatic zones depend on the state and fluctuations of the global climate over different periods of time. According to several studies, there has been a clear trend towards the formation of warmer and drier climates since the middle of the 20th century . If this development continues, it is very likely that there will be a shift in existing climatic zones and the establishment of new ones.
In science it is generally assumed that if the warming continues, considerable consequences for flora and fauna in all climatic zones can be expected. By the year 2100, almost 40 percent of the world's land areas could be affected by the ongoing transformation of the existing climates, with the risk of extensive species loss and large-scale deforestation . Sub-tropical and tropical areas would be particularly susceptible to this change, since, according to paleobiological analyzes, they have only been subject to marginal fluctuations over the past millennia and are therefore less adaptable. One of the most lasting effects of the warming process in the arctic regions would be if the current trend of polar amplification continued in this region. Changes in temperature have considerable effects on the biotopes that exist there. With a further increase in anthropogenic emissions, the Mediterranean region and parts of Chile and California are also greatly affected by this development, with the risk of regional desertification.
In addition to the emerging shift in climatic zones, there are also changes in the distribution of vegetation in mountain ranges in the tropical belt . For example, for the 6,263 meter high Chimborazo in Ecuador, based on a comparison with earlier records, it was found that over the past 200 years, due to glacial melt and increasing global warming, the plant cover has expanded about 500 meters further upwards.
The earth's climate system, which is essentially driven by solar radiation , consists of five main components, also called earth spheres : Earth's atmosphere , hydrosphere , cryosphere , biosphere and lithosphere (with the surface area of the pedosphere ). These are characterized in detail as follows:
- The earth's atmosphere is the gaseous shell of the earth's surface, consisting mainly of nitrogen and oxygen . This is divided into several layers, namely from bottom to top troposphere , stratosphere , mesosphere , thermosphere and exosphere . The weather happens exclusively in the lowest layer ( troposphere ), the vertical extent of which (increasing from the poles to the equator) is approximately 7 to 17 kilometers. The atmospheric greenhouse effect , based on the effects of trace gases such as carbon dioxide and methane , prevents the global surface temperature from falling well below freezing point .
- The hydrosphere encompasses the entire occurrence of liquid water on or under the surface of the earth . Subsystems are the oceanosphere (the water in the seas) and the limnosphere (inland waters on the mainland such as lakes, rivers or groundwater ). The water vapor as a gaseous state of the water does not belong to this category, but is part of the atmosphere .
- The cryosphere includes sea ice , ice shelves , ice sheets , mountain glaciers , ice in permafrost soils , ice crystals in clouds as well as all seasonal and therefore highly variable snow and ice coverages. Since ice surfaces reflect the majority of the incident solar radiation, the growth or shrinkage of the cryosphere is an elementary climate factor that influences the earth's reflectance ( albedo ).
- The biosphere ( "space of life" ) extends from higher atmospheric layers to a few kilometers deep into the earth's crust ( lithosphere ) and is populated exclusively by microorganisms in these "peripheral areas" . Since life depends on interacting with and adapting to the inanimate environment, several ecosystems have emerged on a planetary level in the course of evolution . Due to its complexity and its intensive interactions with other spheres, the biosphere (to which humans also belong) is at the center of many scientific disciplines, especially biology and environmental sciences .
- The lithosphere forms the mainland area of the earth's surface and the ocean floor . Since the uppermost layer of the continental lithosphere is exposed to weathering, simultaneously absorbs or stores air, water and organic substances and often has vegetation, there is a broad-based interaction between it and the other spheres of the earth.
The internal processes and interactions that take place within and between the individual spheres are also part of the climate system. External processes, i.e. processes that do not belong to the climate system, drive the climate system; in addition to solar radiation, these are volcanism and human influences (→ #climate factors ).
As climate elements , the measurable properties of the Earth climate system are referred to that mark individually or through their interaction the climate. These are mostly meteorological quantities that are recorded using weather stations , weather probes or satellites , but also data series from oceanography and various geosciences disciplines . In meteorology , the focus is on spatial data analysis , while in climatology the focus is on time series analysis .
The most important metrics are:
- Air temperature
- Humidity ( dew point )
- Air pressure
- Wind speed and wind direction
- Precipitation type
- Sunshine duration
- Cloud cover
- Global radiation
Climate factors are those components that have a significant physical, chemical or biological effect on the climate system and stabilize, shape or change it over different periods of time. Several factors can interact and in this way reinforce a process or largely neutralize each other as opposing influences.
Climatic factors over the entire duration of the earth's history
- The sun is of primary importance for the earth's climate. 4.6 billion years ago sat with her after a period as a protostar of the fusion process one that present in the solar core hydrogen gradually into helium converts. This stage lasts around 11 billion years, whereby the luminosity and the radius of the star will increase significantly or have already increased. This means that at the beginning of the earth's history, the sun had only 70 percent of its current radiation output. The paradox of the weak young sun touches on fundamental questions about the origin and continuity of earthly life and is a central theme in atmospheric sciences .
- The volcanic activity since the beginning of Earth's history a fundamental driver of climate with very different manifestations (including shield volcanoes , hot spots or Manteldiapire , Magmatic United Provinces ). The permanent release of carbon dioxide through volcanic outgassing (currently around 180 to 440 megatons annually) largely offsets the CO 2 storage caused by weathering and sedimentation and made a decisive contribution to overcoming the snowball-earth stages in the late Precambrian . On the other hand, repeated destabilization of the biosphere due to greatly increased volcanic activity has been clearly demonstrated.
- Greenhouse gases are radiation-influencing gaseous substances in the atmosphere that drive the greenhouse effect , including water vapor , carbon dioxide, methane , tropospheric ozone and nitrous oxide . The most powerful greenhouse gas in its overall effect is water vapor , the share of which in the natural greenhouse effect varies between 36 and 70 percent. Since the atmospheric water vapor content is directly dependent on the air temperature, its concentration decreases at lower average temperatures and increases during a warming phase ( water vapor feedback or Clausius-Clapeyron equation ).
- The plate tectonics in a sense is the driving force for climate change over geological time. Their influence on the earth's climate is not limited to the formation of volcanic zones, mountain formations, the location and size of the continents and the associated weather systems or oceanic currents are also directly related to plate tectonics. Carbon bound in lime , for example, can be released again if such layers are subducted.
- Albedo is the measure of the reflectivity of non-luminous surfaces. Snow and ice surfaces have an albedo of about 0.80 (which corresponds to a reflection of 80 percent), while a free ocean surface albedo comprise of about 0.20 and thus to absorb more heat energy than they reflect. The Earth's mean spherical albedo is currently around 0.3. It depends on the extent of the oceans, ice sheets, deserts and vegetation zones (including cloud cover and aerosol concentration ) and can change along with the radiation balance .
- Weathering processes tend to cool down and come into play to varying degrees depending on the respective climatic condition. Due to chemical weathering, carbon dioxide is permanently withdrawn from the atmosphere andboundin the lithosphere . Part of the stored CO 2 is returned to the atmosphere over millions of years through the outgassing of continental or oceanic volcanoes. Under current geophysical conditions, a complete replacement of atmospheric carbon dioxide based on the carbonate-silicate cycle would take approximately 500,000 years.
- Climate-relevant sea level fluctuations (eustasia) are based on two main causes: 1. Changes in seawater volume due to the binding of water in continental ice sheets or due to their melting (glacial eustasia) ; 2. Changes in the ocean basin volume as a result of tectonic shifts, for example through the formation of new oceanic crust . This enables sea level rises or falls in the range of 100 to 200 meters.
- Cloud formations have a major impact on the earth's energy balance and thus on the climate system. However, the causal relationships have not yet been fully clarified. More recent studies assume the possibility that high CO 2 concentrations could have a negative influence on the formation of stratocumulus clouds , which would mean an additional warming effect.
Sporadic influences over long periods of time
- Magmatic large provinces were often the cause of rapid climate changes. This is the large-volume escape of igneous rocks from the earth's mantle , which sometimes spread over millions of km² and emitted considerable amounts of carbon dioxide and other gases. In contrast to "normal" volcanism, the activities of a magmatic large province did not cause aerosol-related cooling, but global and sometimes extreme warming with additional activation of several feedbacks. Well-known magmatic large provinces are the Siberian Trapp (252 mya) and the Dekkan-Trapp in today's West India (66 mya).
- Organisms that can cause climate-relevant effects through the fixation or release of greenhouse gases, such as corals , methane producers or plants such as the swimming fern Azolla , which probably “colonized” the Arctic Ocean for 800,000 years in the Eocene .
- The ice-albedo feedback describes a positive feedback effect in the climate system, through which the snow and ice cover (especially in the polar regions) continues to increase in the course of global cooling. The ice-albedo feedback is particularly important during the transition from a warm to a cold period, as it accelerates and intensifies the icing and cooling processes.
- Impact events on a large scale can not onlydestabilizethe biosphere to a considerable extent andcausemass extinctions such as that at the Cretaceous-Paleogene border , but also influence the climate over longer periods of time (an abrupt impact winter over several decades, possibly subsequent strong warming lasting severaltimes10,000 years).
- → #Earth orbit parameters .
Additional and currently effective influences
- Sunspot cycles normally correlate with the eleven-year Schwabe cycle and the Hale cycle with a duration of 22 years, whereby the sun can remain in a "standstill phase" for decades. In climatology, there is broad agreement that global warming has completely decoupled from solar activity since the mid-20th century. The extent to which the activity cycles played a role in the course of the “ Little Ice Age ” and other climate anomalies is the subject of a scientific discussion.
- Aerosols are liquid or solid suspended particles linked to a carrier gas, whichare involvedin the formation of clouds in the form of hygroscopic particles as condensation nuclei . In addition, depending on their concentration, chemical composition and atmospheric distribution, they mainly contribute to a cooling of the climate, especially when they occur as bright sulphate aerosols . Aerosols find their wayinto the atmosphere, for example, through volcanism, forest and wild fires and, since the beginning of the industrial age, increasinglythrough anthropogenic emissions.
- Rossby waves (also planetary waves ) are large-scale undulating movements in the atmosphere and the seas (as a wind-controlled factor in oceanic circulation ). In the air envelope, Rossby waves are a meandering form of the jet stream along the border between polar cold and subtropical warm air zones. The change in the atmospheric Rossby waves registered in recent years leads to an increase in stable weather conditions and thus to an accumulation of extreme weather conditions in the middle latitudes of the northern hemisphere.
- The North Atlantic Oscillation ( NAO ) is associated with a change in the pressure conditions between the Icelandic low in the north and the Azores high in the south over the North Atlantic . The NAO has a strong influence on weather and climatic conditions in eastern North America, the North Atlantic and Europe.
- The Atlantic Multi-Decade Oscillation (AMO) describes a cyclical fluctuation of the ocean currents in the North Atlantic with a change in the sea surface temperatures of the entire North Atlantic basin.
- The El Niño-Southern Oscillation (ENSO) is a short-term fluctuation in the Earth's climate system, resulting from unusual warming in the eastern Pacific ( El Niño ) and air pressure fluctuations in the atmosphere ( Southern Oscillation ). The ENSO phenomenon is able to influence global temperature developments in the short term.
- Global warming is the well-established trend towards higher global average temperatures due to anthropogenic greenhouse gas emissions, with consequences such as rising sea levels , glacier melt , shifting climatic zones and an increase in extreme weather conditions . Statements about the extent and duration of the future temperature development are based on various scenarios that can be expected to have significant effects over millennia, and possibly beyond.
In contrast to regional or hemispherical occurring climatic variations (also air fluctuations or climate anomalies , with a period of several decades or centuries) a global carried climate change through the striking change in the radiation drive , which the earth system of a thermal-radiative equilibrium transferred to a new equilibrium. Depending on the geophysical constellation, this process causes a significant cooling or a strong warming over different periods of time. The current global warming caused by humans is an example of a rapidly advancing but not yet completed climate change, the previous and predicted course of which may represent a unique event in climate history for which no equivalent exists.
The most important components of climate change on a global level are the varying solar radiation due to the Milanković cycles , the reflectivity ( albedo ) of the entire earth's surface and the atmospheric concentration of greenhouse gases , predominantly carbon dioxide (CO 2 ) and methane (CH 4 ), which in turn depend on the Influence the strength of the temperature-dependent water vapor feedback on the basis of the greenhouse effect. The climatic condition of the last 2.6 million years ( Quaternary Cold Age ) was that of an Ice Age and was mainly controlled by the Milanković Cycles, which significantly changed solar radiation over a period of 40,000 or 100,000 years and thus triggered the change in the cold ages ( Glacials) with warm periods (interglacials).
Carbon dioxide and / or methane were not always the main drivers of climate change. In the context of natural climate change events, they sometimes acted as “feedback links” that strengthened, accelerated or weakened a climate trend. In this context, in addition to the earth's orbit parameters , feedback such as ice-albedo feedback , vegetation cover , weathering processes , the variability of the water vapor content and a large number of geological and geophysical influences must be taken into account.
Abrupt climate changes are a special form of climate change . In the history of the earth, they have been triggered by impact events , eruptions of super volcanoes , large-scale magma outflows , rapid changes in ocean currents or by rapid feedback processes in the climate system, often in connection with ecological crises.
The earth formed from several protoplanets of different sizes 4.57 billion years ago . According to the collision theory , it is said to have obtained its current mass from a collision with a Mars-sized celestial body called Theia 4.52 billion years ago. As a result, parts of the earth's mantle and numerous fragments of Theia were thrown into orbit , from which the initially glowing moon formed within 10,000 years . Due to the lack of usable climatic data, no reliable statements can be made about this earliest and chaotic stage in the history of the earth. Only from 4.0 to 3.8 billion years ago, after the formation of the oceans and the first forms of life, did fossil traces and proxies (“climate indicators”) allow conclusions to be drawn about climatic conditions. On the basis of this evidence, it is assumed that a relatively warm climate prevailed over large parts of the Archean . This phase ended in the early Proterozoic 2.4 billion years ago with the transition into the 300 million year Paleoproterozoic glaciation .
Towards the end of the Precambrian , oxygen diffused in large quantities into the stratosphere and an ozone layer was formed based on the ozone-oxygen cycle . From then on, this protected the earth's surface from solar UV radiation and made it possible for the continents to be colonized by flora and fauna. Oxygen levels increased rapidly during the ancient times . In the vicinity of the Devonian - Carboniferous border (approx. 359 mya) it corresponded for the first time to today's concentration of 21 percent and reached around 33 to 35 percent towards the end of the Carboniferous. In the further course of the earth's and climatic history, the atmosphere was repeatedly subject to strong changes, depending on biogeochemical and geophysical influences. The proportions of oxygen, carbon dioxide and methane fluctuated considerably in some cases and played a decisive role, either directly or indirectly, in a number of climate change events.
When analyzing climate history, a growing body of evidence supports the assumption that almost all known mass extinctions or the significant reduction in biodiversity were linked to rapid climate changes and their consequences. This led to the realization that these events do not necessarily have to be linked to long-term geological processes, but have often taken a catastrophic and time-limited course. Biological crises have correlated several times in the last 540 million years with a cooling phase (with a global temperature drop of 4 to 5 ° C), but more often with strong warming in the range of 5 to 10 ° C. In the latter case, a bundle of side effects (decline in vegetation, outgassing of toxins and pollutants, oxygen deficits, acidification of the oceans, etc.) contributed to further destabilizing the terrestrial biosphere.
The radiometric dating developed in the 20th century , which allows an absolute age determination of igneous rocks and volcanogenic sediments , led to the establishment of the sub-disciplines geochronology and chronostratigraphy and is of great importance for all periods of the 541 million years long Phanerozoic and beyond. Current methods in use are uranium-thorium dating and uranium-lead dating . For exact dating, zirconium crystals are particularly suitable , the stable lattice structure of which allows precise evaluation of the radioactive nuclides enclosed therein . In addition, a number of different isotope studies are used to reconstruct past climates and their environmental conditions , with the help of which, for example, previous sea temperatures, CO 2 concentrations or changes in the carbon cycle can be determined. Further analysis tools are used for more recent geological periods ( Pleistocene and Holocene ). Among the most important are the dendrochronology (annual ring analysis), palynology (pollen analysis), varven chronology (band tone dating), ice cores , oceanic sediments and stalactites ( stalagmites and stalactites ).
Climatic events in historical times and their effects on human societies are the subject of research in historical climatology or environmental history , whereby written records are often used. Central Europe has such a rich fund of contemporary reports that from around the year 1500, meaningful descriptions of the weather at that time are available for almost every single month. Climate changes such as the Medieval Climate Anomaly or the Little Ice Age are subjected to a scientific analysis, as are individual extremes, for example the year 1540, which was marked by a catastrophic drought .
The fact that long-term fluctuations in the global climate could be based on cyclical changes in the earth's axis and orbit was already suspected in the second half of the 19th century. The geophysicist and mathematician Milutin Milanković (1879–1958) succeeded in making a first comprehensive presentation on the basis of extensive calculations . His explanatory model, created over years of work, takes into account the periodic changes in the earth's orbit (from slightly elliptical to almost circular), the inclination of the earth's axis and the gyrating of the earth around its axis of rotation ( precession ).
The cycles named after Milanković influence the distribution and partly the intensity of solar radiation on earth. Above all, the large cycle controlling the eccentricity with a duration of 405,000 years formed a stable cosmic "clock generator" over large parts of the Phanerozoic and, according to more recent findings , can be traced back to the Upper Triassic about 215 million years ago. The cycles had a lasting effect, especially during different glacial phases with low greenhouse gas concentrations, whereby their influence on the course of the Quaternary Glaciation can be easily understood due to their temporal proximity. However, since the Milanković cycles are too weak to be considered as the primary drive for the entire climate history, they seem to function primarily as “impulses” in the climate system. When modeling climate processes, additional factors and feedback effects are therefore taken into account.
Since its “revival” in the 1980s, the theory has become an integral part of paleoclimatology and Quaternary research in a modified and expanded form . The Milanković cycles are considered to be an important influencing factor in current climate research and are used both in the reconstruction of the last phases of the cold period and in the analysis of further climate change events during the Phanerozoic .
According to a frequently used definition, climate sensitivity is that temperature increase that occurs when the atmospheric carbon dioxide concentration doubles . In relation to the current global warming , this would mean a CO 2 doubling from pre-industrial 280 ppm to 560 ppm. As of 2019, the CO 2 concentration , which fluctuates slightly over the course of the year, is around 412 ppm. In addition to carbon dioxide , other gases are involved in the greenhouse effect , the contribution of which is usually represented as CO 2 equivalents .
The limitation of the climate sensitivity to the most precise temperature value possible is of fundamental importance for the knowledge of the future climate development. If only the radiation effect of CO 2 measured in the laboratory is considered, the climate sensitivity is 1.2 ° C. However, a number of positive feedback effects in the climate system also contribute to climate sensitivity, with a distinction being made between fast and slow feedback. Water vapor , ice albedo and aerosol feedback as well as cloud formation are among the fast feedbacks. The ice sheets , carbon- binding weathering processes as well as the expansion or reduction of the vegetation area are considered to be slow feedback effects and are assigned to the Earth system's climate sensitivity .
The climate sensitivity as a dynamic factor depends to a large extent on the respective climate condition. Examples from geological history show that climate sensitivity also increases with the increase in radiative forcing and the associated increase in global temperature. For example , a climate sensitivity in the range of 3.7 to 6.5 ° C is postulated for the strong warming phase of the Paleocene / Eocene temperature maximum 55.8 million years ago. Similar high values are estimated for most of the rest of the Cenozoic .
In the past few decades, very different values have been assigned to climate sensitivity. The status reports of the Intergovernmental Panel on Climate Change (IPCC), which summarize the current state of research, are considered to be an authoritative and reliable source. In the Fourth Assessment Report published in 2007, the temperature corridor classified as “likely” was between 2 and 4.5 ° C. According to the Fifth Assessment Report published in 2013, the range was between 1.5 and 4.5 ° C. Accordingly, the best mean estimate for the current climate sensitivity is around 3 ° C. In 2019, the first evaluations of the newly developed climate model series CMIP6 showed that some standard tests with 2.8 to 5.8 ° C resulted in significantly higher climate sensitivities than earlier model generations. However, the application of CMIP6 with the model variant CESM2 (Community Earth System Model version 2) led to considerable deviations or unrealistic values when compared with paleoclimatologically determined temperature data from the early Cenozoic era.
Human climate factor
Since the beginning of industrialization in the 19th century, people have increased the proportion of greenhouse gases in the atmosphere to a significant extent. The burning of fossil fuels in particular contributed to the fact that the carbon dioxide concentration rose from 280 ppm (parts per million) to the current (2020) 415 ppm. In addition, there are considerable methane emissions, mainly caused by intensive animal husbandry , and other greenhouse gases such as nitrous oxide (laughing gas) or carbonyl sulfide . Another important factor is the extensive deforestation, especially of the tropical rainforests . According to the Intergovernmental Panel on Climate Change (IPCC), the temperature increase compared to the pre-industrial period up to 2018 was around 1.0 ° C. By the end of the 21st century, the IPCC expects in the worst case ( representative concentration path RCP 8.5) a temperature increase in the range of 2.6 to 4.8 ° C. The unanimous scientific opinion is that the increase in greenhouse gases and the associated rise in temperature can be attributed to human activities. If it is not possible to reduce anthropogenic emissions to a large extent, there is a risk of numerous and sometimes serious consequences , even with a relatively moderate warming of 2 ° C , including rising sea levels, increasing weather extremes and serious effects on human communities. More recent analyzes based on extensive palaeoclimatological data series from the last 12,000 years come to the conclusion that the warming that has occurred in the 21st century to date has a high probability of exceeding the temperature values of the Holocene optimum climate (about 8,000 to 6,000 years ago).
Rocking members ( English Tipping element ) are in the Earth System Research components of the air conditioning system, which assume a new state by low external influences when a specific tilting point reach. These changes can occur abruptly and are sometimes considered irreversible. The concept of the tilting elements has been widely discussed in the geoscientific literature since the beginning of the millennium as a previously neglected possibility of discontinuous processes - especially in connection with the current global warming.
In an initial inventory, the following potential tipping elements were identified:
- Melting arctic sea ice in summer
- Melting of the Greenland ice sheet
- Melting of the West Antarctic ice sheet
- The Atlantic thermohaline circulation slows down
- Change in the El Niño-Southern Oscillation (ENSO)
- Collapse of the Indian summer monsoon
- Changes in the West African monsoon system affecting the Sahara and the Sahel zone
- Desertification of the tropical rainforest
- Reduction of boreal forests
In the following years, other tipping elements were named, including the release of methane from the oceans and from thawing permafrost as well as the worldwide death of coral reefs . By activating some tilting elements, additional tipping points could be exceeded in the form of feedback. There would therefore be the risk of a chain reaction (“cascade”) that would irreversibly transform the climate into a warm climate , roughly comparable to the environmental conditions of the Pliocene or - if the emission volume remains unchanged - the Eocene .
With regard to different geochronological periods, there are a number of clear indications that when certain tipping points were reached an abrupt change to a new climatic state took place, such as during the Hangenberg event in the late Devonian about 359 million years ago.
Climate models are computer models for calculating the climate and its influencing factors over a certain period of time and are used both for the analysis of future developments and for the reconstruction of paleoclimate. The projections of the climate models are naturally more uncertain than those of the weather models, since much longer periods of time have to be taken into account and a number of additional parameters must be taken into account. For this reason, no climate forecasts are created, but scenarios with specific probability corridors. A climate model is usually based on a meteorological model , as is also used for numerical weather forecasting . However, this model is modified and extended for climate modeling in order to correctly map all conservation quantities. Often an ocean model , a snow and ice model for the cryosphere and a vegetation model for the biosphere are coupled.
Most of the models are calibrated on real climatic processes of the present and the past, so that they can not only reproduce current developments, but also, for example, the climate cycles over several 100,000 years. This made it possible to put the characteristic course of the Quaternary Ice Age with its warm and cold phases, including the Milanković cycles , the greenhouse effect and the ice-albedo feedback , on a solid theoretical foundation. However, for projections of future climate developments over centuries or longer there are great uncertainties with regard to possible feedback processes, especially in connection with the tipping elements in the earth system , so that it is difficult to achieve valid results even when taking into account the climate history or paleoclimatologically determined data. Decadal climate models are also only of limited informative value , as fluctuations that occur at short notice can overlay or falsify a trend at any time.
Climate in Germany
Germany lies entirely in the moderate climatic zone of Central Europe in the area of the west wind zone and is in the transition zone between the maritime climate in Western Europe and the continental climate in Eastern Europe . The mild climate for the relatively high northern latitude is influenced , among other things, by the Gulf Stream .
The nationwide regional mean air temperature is 8.2 ° C (normal period 1961–1990), the lowest monthly average is reached in January at −0.5 ° C and the highest at 16.9 ° C in July. The Upper Rhine Graben is the front runner in terms of annual average temperatures with over 11 ° C, while Oberstdorf , 800 meters above sea level, records around 6 ° C. The coldest place is the summit of the 2962 m high Zugspitze with an average annual temperature of almost -5 ° C. The mean annual precipitation is 789 mm, the mean monthly precipitation is between 49 mm in February and 85 mm in June. The amount of precipitation fluctuates in a range of over 1000 mm in the Alpine region and the low mountain ranges and below 500 mm in the rain shadow of the Harz between Magdeburg in the north, Leipzig in the east and Erfurt in the south. In general, the humidity decreases from west to east.
In the last few decades Germany has also seen a clear warming trend: According to the statistics of the German Weather Service , the average temperatures have been above the long-term average of 8.2 ° C in all years since 1988 (except for 1996 and 2010). In 2014, a double-digit annual value was achieved for the first time with 10.3 ° C, only exceeded by the previous record year 2018 with 10.5 ° C. For the period from 1881 to 2018, the evaluations by the German Weather Service show a temperature increase for Germany of +1.5 ° C (linear trend). The increase in summer was +1.4 ° C (1881–2018), in winter +1.5 ° C (1882–2019). The trend has intensified over the past few decades. Associated with this, observations of plant development show a shift in the phenological seasons . For example, the hazelnut blossom , which is defined as an indicator for the phenological early spring, occurred approx. 12 days earlier in the period 1991–2010 than in the period 1961–1990. Even migratory birds are almost a month longer in Germany than in the 1970s.
The lowest temperature ever recorded in Germany was recorded on December 24, 2001 at −45.9 ° C at Funtensee in the Berchtesgaden Alps . However, this is a particularly exposed location, as cold air can build up in the drainless depression above snow cover. The German Weather Service gives the official record value of -37.8 ° C, measured on February 12, 1929 in Hüll (district of Wolnzach, Pfaffenhofen district). After the highest temperature to date of 40.5 ° C was measured in Geilenkirchen in North Rhine-Westphalia on July 24, 2019 , Lingen in Lower Saxony set a new record one day later with 42.6 ° C. Unusually high temperatures occurred in a number of other locations on July 25, 2019.
The sunniest regions of Germany can be found in the northern and southern peripheral areas of the country. With 1869 hours of sunshine per year, Cape Arkona on the island of Rügen is the record holder for the current reference period 1981-2010. In the south are the sunniest regions on the southern Upper Rhine, in the region around Stuttgart and in the Bavarian Alpine foothills including the state capital Munich . In these areas, an average of 1800 hours of sunshine are measured annually. However, their distribution is very different with regard to the seasons: While most hours of sunshine occur on the Baltic Sea coast in spring and summer, the winter months in the south and especially in the Alpine foothills are significantly sunnier than in the other parts of the country.
Weather conditions such as pronounced droughts or heat waves have so far been relatively rare due to the compensating westerly wind zone, but occurred not only in Germany but almost everywhere in Europe in the course of 2018 and, according to various studies, could increase in the future. The opposite extreme was a Europe - wide cold phase lasting from late January to mid-February 2012 . In the autumn and winter months, there are always individual storms or hurricane lows, which mostly move east across the North Sea and mainly hit northern Germany and the low mountain ranges, such as the hurricane lows Lothar in December 1999 and Kyrill in January 2007. Occur regularly There are also floods, which after intense rainfall in summer ( Oder floods 1997 , floods in Central Europe 2002 ) or after snowmelt can lead to floods with considerable potential for damage. Droughts normally affect the rather dry north-east of Germany, but can sometimes spread to the whole country, such as during the heat waves in 2003 , 2015 and 2018 .
Other extreme weather such as thunderstorms and tornadoes occur mainly in early and midsummer. While southern Germany is mainly hit by hailstorms , the tornado tendency increases slightly to the northwest. A special feature here are mainly occurring on the North and Baltic Sea coast in late summer waterspouts . A total of 30 to 60 tornadoes can be expected annually, in some years significantly more (119 tornadoes in 2006).
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